CSLB C-46 Solar ContractorPhotovoltaic System InstallationHard
A solar technician is installing a string inverter that requires dedicated AC overcurrent protection. The inverter's continuous output current rating is 20A. According to NEC 690.8(A)(1) and 690.9(A), what is the minimum standard overcurrent protection device (OCPD) rating required for this inverter's AC output circuit?
- A30A
- B20A
- C35A
- D25A
Show answer & explanationAnswer & explanation
Correct answer: A. 30A
NEC 690.8(A)(1) requires that the continuous output current of an inverter be multiplied by 125% to determine the minimum required ampacity for the conductors and the minimum continuous current rating for the OCPD. So, 20A * 1.25 = 25A. Then, NEC 690.9(A) states that the OCPD must be sized to the next higher standard rating if the calculated value does not correspond to a standard rating. The next standard OCPD rating above 25A is 30A.
Why the other options are wrong
- B. 20A is the inverter output, not the minimum OCPD rating after applying the 125% rule and rounding up to a standard size.
- C. 35A is higher than the minimum required standard rating, though it would also be permissible.
- D. 25A is the minimum *calculated* value (20A * 1.25), but it's not a standard OCPD rating, so you must go to the next higher standard size.
NEC 125% Rule (PV OCPD Sizing)
Requires overcurrent protection devices (OCPDs) for PV circuits to be sized at not less than 125% of the maximum continuous current, then rounded up to the next standard OCPD size.
- Ensures OCPDs can handle continuous loads without nuisance tripping.
- Protects conductors and equipment from overcurrents.
- Requires knowledge of standard OCPD sizes (e.g., 15, 20, 25, 30, 35, 40, 50A).
Memory trick: Multiply by 1.25, then round up, for safe circuit setup!